http://rgooglemaps.r-forge.r-project.org/OfflineMaps-RgoogleMaps-leaflets.html
http://rgooglemaps.r-forge.r-project.org/Light_spatial_data_visualization.html http://rgooglemaps.r-forge.r-project.org/Mapview.html
http://rgooglemaps.r-forge.r-project.org/Serious_spatial_data_visualization.html